Early in 2001, MgB2 was discovered as a boron compound having a superconductivity transition temperature of 39 K and it is expected to find applications in the manufacture of superconducting wires and thin films. Synthesis of MgB2 involves difficulty due to the high vapor pressure of Mg.
The present invention relates to a wire preparing technique that is essential to commercial application of MgB2 and it also relates to a technique for preparing thin films of MgB2 that are required to put this compound into device form. According to the invention, a molten mixture of magnesium chloride, sodium chloride, potassium chloride and magnesium borate is treated by an electrochemical technique at 400° C. or above to prepare a superconducting wire or thin film of a boron compound MgB2 that shows zero resistance at a superconductivity transition temperature of about 39 K or below.
The following three techniques are known to be capable of preparing superconducting wires of MgB2 and the thin films that are required to put MgB2 into device form: 1) subjecting solid Mg and B samples to high-temperature reaction in vacuum; 2) performing a similar reaction in a closed system as in a quartz or stainless steel tube either evacuated or filled with an inert gas such as argon; 3) evaporating Mg at high temperature in vacuum so that its vapor is deposited on a B target for reaction.
In order to perform heating in vacuum or in an evacuated closed system, not only a vacuum pump that usually costs at about 200,000 yen but also an apparatus capable of heating up to about 900–1000° C. which are high enough to carry out the reaction of a mixed solid sample must be used. There is no need to use a vacuum pump if the reaction is performed under an inert gas but even in this case a heating apparatus of the type described above is necessary.